True to the meaning of its name,
a ko-dama is the spirit of a tree. Not all trees have ko-dama dwelling
in them, however, and usually these entitites tend to inhabit trees
of very great age or size. It is said a person who cuts down a tree
with a ko-dama living in it will bring calamity upon their entire village,
and often the sacred rope called shimenawa
is wound around trunks thought to contain these spirits in order to
protect them.

While ko-dama are generally invisible to human eyes, they are thought
to mischievously play with and mimic human voices, creating echos in
the forest. "Echo" has also come to be another meaning of
the word kodama.